Thermoplastic elastomers are well known in the art and are available commercially. An important class of thermoplastic elastomers is styrenic block copolymers. These block copolymers are typically characterized by at least two polymer blocks of primarily polymerized monovinyl aromatic hydrocarbon monomers separated by at least one elastomeric polymer block, such as a polyolefin or (an optionally hydrogenated) polymer block of primarily polymerized conjugated diene monomers. Their behavior is explained on the basis of the so-called domain theory, wherein the poly(monovinyl aromatic hydrocarbon) polymer blocks cluster together and the elastomeric polymer blocks form a separate rubber phase that is the matrix.
Upon heating of a styrenic block copolymer above the glass-transition temperature of the poly(monovinyl aromatic hydrocarbon) blocks (about 95° C. in case of polystyrene), the viscosity and the elasticity of the block copolymer remains high compared to a homopolymer of the same molecular weight due to non-Newtonian behavior of the melt. This behavior is attributed to the persistence of a two-phase “domain” structure found in the melt below the so-called order-disorder transition temperature. In such a domain structure, flow can only take place by the poly(monovinyl aromatic hydrocarbon) polymer blocks of the block copolymer being pulled out of the domains.
Selectively hydrogenated block copolymers containing at least two mostly non hydrogenated poly(monovinyl aromatic hydrocarbon) blocks, e.g. polystyrene blocks, separated by at least one partially to completely hydrogenated conjugated diene block have very high and very non-Newtonian viscosities because of their extreme segmental incompatibility. Accordingly, processing is difficult and must take place under high shear conditions.
In many practical applications, the hydrogenated styrenic block copolymers are mixed with other ingredients being compatible with the rubber phase, compatible with the poly(monovinyl aromatic hydrocarbon) phase or simply being easily dispersed with the block copolymer system.
Styrenic block copolymers have also been used in the field of fiber optics. Fiber optic cables are an increasingly important technology in communications. The cables are made up of a core of optical fibers surrounded by a sheath that encompasses and protects them. A protective layer of material is provided between the inner and outer layers of the cable. Often a tape can be provided around the protective material along with some metallic or hard layer to contain the material. Moreover, the cable is usually encased in a plastic jacket for added protection and durability.
Traditionally, the layer of protective material around the fiber core has been made up of a composition composed of oil and styrenic block copolymers. Such a system has been used based on Kraton G polymers, for example as disclosed in U.S. Pat. No. 4,464,013. In these fiber optic systems where the fill material is based on styrenic block copolymers, a large portion of the composition is comprised of the hydrocarbon oil. This facilitates flow of the polymer composition and permits pumping of the material into the fiber optic cables during their formation.
A drawback however is that when the cables are cut, the grease or oil drips from the cables. Accordingly, when cutting or repairing the cables, this oil from the polymer composition must be cleaned off the fibers. Although efforts are made to improve the consistency of such compositions, they still tend to be greasy or oily. Accordingly, this can lead to difficulty when working on such cables as a residue may be left behind or make clean-up more problematic. Therefore, although such compositions are easy to pump in small diameter fiber optic cables, they are not user-friendly. Dry gels are much easier for operators to work with, however, they are difficult to pump or introduce into the fiber optic cables.
Therefore, what is needed is a composition that can be pumped into a fiber optic cable as a protective material in fiber optic cables, yet reduces or avoids the difficulties associated with oil leakage and cleanup.